Parkinson's disease (PD) is a neurodegenerative disorder that causes slowed movements, tremor, rigidity, and a wide variety of other symptoms. "Neurodegenerative" refers to the degeneration, or death, of neurons, the type of cell in the brain that is the basis for all brain activity.
Parkinson's disease occurs when neurons (nerve cells) in a part of the brain called the substantia nigra degenerate, or die off. The loss of these cells disrupts the brain's normal control of movement, causing the person to experience slowed movements, stiffness or rigidity, and tremor.
PD is one of the most common neurodegenerative diseases, second only to Alzheimer's disease in the number of people affected. Estimates suggest that approximately 750,000 Americans have PD. It affects older people much more than younger, and indeed, old age is the single greatest risk factor for PD.
The average age at diagnosis is 62. Onset before age 40 is extremely rare. Men are slightly more likely to be affected than women.